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  <script>
    Array.prototype.sum = function () {
      var sum = 0;
      for (let i = 0; i < this.length; i++) {
        sum += this[i]
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    var arr = [12, 3, 23, 5, 8, 56, 34, 23];

    var s = arr.sum()
    console.log(s);
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